notifications 5.x-1.2

Some new features and performance improvements:
- Backported help text for Inmediate sending, #330786
- Digesting options per interval and support for digesting plug-ins.
- New digest format, 'Long', to print out the whole event.
- Reworked message templating and digesting, added tests.
- Performance improvements for taxonomy subscriptions (and groups).
- Improved query builder to support fields with array values.
- Simpletest update, moved tests around, did some clean up.